In the field of safety inspection, substance identification, and identification of contraband such as drugs and explosives in particular, are of great significance.
For the detection of explosives concealed in large articles such as containers, two basic conditions are required: strong penetrability, that is, capable of penetrating the iron sheet of a container and reaching certain depth of the inspected object; and capable of obtaining the characteristic information of the explosives, for example, elemental composition.
The principles of substance identification by the radiation inspection system based on X-ray sources consist in identifying with different absorption curves of X-rays of substances with different atomic coefficient elements, and it is necessary to use X-rays having two or more energies to perform simultaneous imaging. This radiation inspection system may distinguish between substances with a high atomic coefficient and substances with a low atomic coefficient, and further distinguish between organics and inorganics.
In addition, contraband may be inspected by a neutron-based radiation inspection system. The neutron has a strong penetrating ability. At the same time, by detecting and analyzing the energy spectrum releasing γ rays after neutrons react with the inspected object, it is possible to detect whether contraband are present or not. The neutron-based radiation inspection system is capable of penetrating large articles and performing elemental analysis. Therefore, the use of a neutron inspection manner to inspect contraband such as explosives or drugs in large articles has great advantages.
In the process of detecting contraband in a neutron inspection manner, elemental analysis techniques are used to judge the elemental composition of organics. Substance identification is performed using the interaction of neutrons and substances, and based on the elemental content characteristics of the contraband and the reaction mechanism of neutrons and nuclei, the elemental composition and proportional relationship of organics such as H, C, N, O and Cl in a substance, to identify the substance and achieve the purpose of inspecting contraband.
Take the inspection of explosives and drugs as an example:
For inspection of explosives, the elemental composition of explosives usually consists in C, H, N and O, and has the characteristics of high content of N and O, and low content of H and C. Whether the explosives are present or not may be detected by detecting and analyzing the energy spectrum of released γ rays after neutrons react with the inspected object.
For inspection of drugs, in the preparation process of many drugs, since it is necessary to involve chlorine-containing substances, such as hydrochloric acid, chloroform, methylene chloride, dichloroethane, and dichloroethylene, chlorine may also be found in many manufactured drugs. By analyzing the proportional relationship of elements such as H, N, and Cl, the possibility of presence and kind of drugs/precursor substances are judged.
In the existing radiation inspection system, some inspect the inspected subject by a fan beam, and some inspect the inspected subject by a pencil beam. However, neither of them can incorporate the inspection efficiency and the inspection accuracy.